Lecture 12: PREDATION and PARASITISM Trophic - the movement of energy through the system Predation: - Predation is a key limiting factor - Refers the ability to occupy a particular space influenced by predator (unless it is the apex predator at the lowest levelfl - Interaction where one species, the predator (consumerfl, kills and eats the other (the preyfl. This is an example of a +/ -. - Predation occurs across the board - e.g. between thrushes and snails, dragonflies and smaller insects and horses and grass (herbivoresfl - Animal-animal,, inter- and intraspecific (cannibalismfl - Animal-plant (herbivoryfl Trophic structure - Feeding relationships between organisms in a community - Key factor in community dynamics for energy flow and nutrient cycling - Consumers feed on energy from the primary producers - There is a constant production and flow of energy through the system Route of energy flow - Trophic levels divide the system and determine the flow of energy and cycling of nutrients - Food chains link trophic levels from producers to top carnivores - Detritivores/decomposers (saprophagesfl - these derive their energy from consuming dead matter - they are responsible for recycling nutrients locked in other organisms - e.g. worms woodlouse, fiddler crab and bettles. - Bacteria and fungi also are considered to be detritivores. - Food webs represent the complexity of feeding relationships in an ecosystem - typically not as simple as in an unbranched food chain. What limits a food chain? - Food chains cannot be longer than 5 trophic levels (Freeman, 2005fl - Energetic hypothesis - suggests that length is limited by inefficient energy transfer - energy is lost from one trophic level to another therefore this is relatively inefficient - Dynamic stability hypothesis proposes that long food chains are less stable than short ones - argue stability is an important element. The longer the chain, the less stable the food chain is - Most data support the energetic hypothesis Quaternary, tertiary, & secondary consumers Tertiary 8 secondary consumers Secondary 8 primary consumers Primary consumers Producers (plants)
Energy loss: - Energy is always lost in the form of heat and cellular respiration - When energy flows as organic matter through an ecosystem, much of it is lost at each link in the food chain - Approximately, 10% of potential energy stored in organic molecules at one trophic level fuels growth and development of organisms at the next trophic level (Rule of Tenfl. - An energy pyramid shows loss of energy from the base towards the top - represents the cumulative loss of energy from an ecosystem. - Energy is lost at every stage - which (as shown through Energetic Hypothesisfl limits the number of trophic levels Tertiary consumers - Higher up in the food chain, there are fewer organisms around, and consume entire packages of fat, protein, etc in order to survive - the prey needs to have high energy - higher predators exist at lower densities. Secondary consumers Primary consumers - Assumes 10% efficiency of energy transfer across